Reduced voltage losses yield 10% efficient fullerene free organic solar cells with >1 V open circuit voltages. Issue 12 (16th November 2016)

• Record Type: Journal Article
• Authors: Baran, D.; Kirchartz, T.; Wheeler, S.; Dimitrov, S.; Abdelsamie, M.; Gorman, J.; Ashraf, R. S.; Holliday, S.; Wadsworth, A.; Gasparini, N.; Kaienburg, P.; Yan, H.; Amassian, A.; Brabec, C. J.; Durrant, J. R.; McCulloch, I.
• Is Part Of: Energy & environmental science. Volume 9:Issue 12(2016)
• Page Start: 3783
• Page End: 3793
• Publication Date: 2016-11-16
• Subjects: Energy conversion -- Periodicals; Fuel switching -- Periodicals; Environmental sciences -- Periodicals; Environmental chemistry -- Periodicals; 333.79
• DOI: 10.1039/c6ee02598f
• Languages: English
• ISSNs: 1754-5692

Abstract

Abstract : Non-fullerene acceptors with optimized energy levels enable 10% efficient solar cells with reduced voltage losses <0.6 V. Abstract : Optimization of the energy levels at the donor–acceptor interface of organic solar cells has driven their efficiencies to above 10%. However, further improvements towards efficiencies comparable with inorganic solar cells remain challenging because of high recombination losses, which empirically limit the open-circuit voltage ( V oc ) to typically less than 1 V. Here we show that this empirical limit can be overcome using non-fullerene acceptors blended with the low band gap polymer PffBT4T-2DT leading to efficiencies approaching 10% (9.95%). We achieve V oc up to 1.12 V, which corresponds to a loss of only E g / q − V oc = 0.5 ± 0.01 V between the optical bandgap E g of the polymer and V oc . This high V oc is shown to be associated with the achievement of remarkably low non-geminate and non-radiative recombination losses in these devices. Suppression of non-radiative recombination implies high external electroluminescence quantum efficiencies which are orders of magnitude higher than those of equivalent devices employing fullerene acceptors. Using the balance between reduced recombination losses and good photocurrent generation efficiencies achieved experimentally as a baseline for simulations of the efficiency potential of organic solar cells, we estimate that efficiencies of up to 20% are achievable if band gaps and fill factors are further optimized.